This invention relates to expendable case ammunition, that is, ammunition which is entirely expelled from the chamber and through the barrel of a firearm, and whose case separates from projectiles contained therein after leaving the chamber of the weapon. This eliminates the need to extract and eject a spent case from the chamber of the firearm. Examples of expendable case ammunition appear in U.S. Pats. Nos. 3,527,137 issued Sept. 8, 1970 to John J. Scanlon; 3,724,376 issued Apr. 3, 1973 to Martin W. Kordas et al; and 3,741,122 issued June 26, 1973 to Martin W. Kordas, all of which are assigned to the owner of the present application. Such ammunition has many of the advantages of true caseless ammunition, in that it eliminates the costly metal cases of conventional cartridges, or metal heads of conventional shotshells, and simplifies the firearm mechanism. At the same time, it tends to overcome many objections to caseless ammunition, including its fragility, its susceptibility to damage by moisture, the risk of accidental ignition by smokers or by a hot firearm chamber, and the difficulty of forming the propellant to precise dimensions.
According to certain prior work in this field, the propellant may either consist of a solid molded propellant disc containing a percussion-responsive primer pellet, or a hybrid arrangement of loose, granular propellant enclosed in the rear of the case by a molded wafer including propellant and primer compounds. Examples of both types appear in the aforementioned U.S. Pat. No. 3,741,122. The molded propellant disc might consist of powder grains coated with a thermoplastic material such as polyvinyl acetate, and consolidated by compression forming in a heated mold. The molded disc gives the primer a sufficiently rigid support to obtain reliable initiation.
There are several objections to this general approach, however. A propellant disc or wafer is expensive to mold, and is rather fragile for the rough handling to which ammunition is often subject in the field. Further, its exposure at the rear of the case, necessary for initiation by a firing pin, does not resolve the problems of absorption of moisture and of accidental ignition. It is preferable to enclose loose propellant.
An earlier form of expendable case ammunition appears in U.S. Pat. No. 1,191,357 issued July 18, 1916 to Parke T. Snyder. Here, the base of a soft lead case was enclosed by a combustible celluloid disk which would be consumed by the burning propellant. The primer was supported at the center of the celluloid disk by a bridge insert attached to the casing. An extraction rim integrally formed in the lead casing would be deformed to bore diameter as the case was discharged from the chamber. Such a case would suffer from excessive weakness to resist propellant pressures, an objectionably high weight and cost, and the difficulty of handling it without causing permanent deformations which would prevent it being chambered. Further, the low average cross-sectional density resulting from making the projectile integral with a lead case would not give the most desirable ballistic characteristics.
An expendable artillery shell case suitable for use with loose, granular propellant appears in U.S. Pat. No. 3,696,749 issued Oct. 10, 1972 to John J. Scanlon and assigned to the owner of the present invention. This design incorporates a flash tube extending centrally through a main propellant chamber, a primer mounted in a plastic base cap which is vented, molded discs of fast-burning propellant located in the cap vents and connected by lengths of fuse to the primer, polyester film to protect the vents, and flexible metal flaps which cover the vents and are bent outwardly by gas pressure on firing. Such a design is feasible for an artillery shell, but the parts are complex and costly, and the assembly steps required are involved; thus such a design could not be used economically in small-caliber cartridges or shotgun shells, even if it were practical to reduce such an assembly to the small dimensions required while retaining sufficient structural integrity to hold the parts together under gas pressures of the same order of magnitude as those generated in an artillery shell.
It is the general object of this invention to provide improved expendable case ammunition. More specific objects include the reduction of the risks of premature ignition of, and accidental damage to, expendable case ammunition; improvement of the reliability of initiation of this ammunition; and simplification of its manufacture. Another object is to provide improved ammunition of this type which is suitable for use with loose, granular propellant. Further objects and advantages will appear as the following description proceeds.
Briefly stated, according to a preferred embodiment thereof, we carry out the invention in part by forming an ammunition case from at least two components, comprising a body defining a forward projectile chamber and a rearward propellant chamber separated by a transverse wall, and an imperforate cap snap-fitted onto the rear chamber. A third component comprising a projectile container is snap-fitted onto the front of the body for use of the case as a shotshell, but this may be omitted when the case is used with a single bullet. These parts are made of a deformable material, such as plastic or metal. The cap is imperforate, but has a thinned diaphragm portion, which may be reinforced by ribs. A primer is formed on the diaphragm portion to lie within the propellant chamber, so that it is fully enclosed by the assembled case. An anvil is integrally formed in the wall of the propellant chamber, preferably extending axially of the case from the transverse wall, and extends into proximity to the front surface of the primer. To initiate the primer, a firing pin penetrates the diaphragm region of the cap and impacts the primer against the anvil. The explosion of the primer is in itself sufficient to rupture the diaphragm portion of the cap, opening the propellant chamber prior to or concurrent with the ignition of the propellant. This ensures that the subsequently-generated gas pressure can escape rearwardly without tearing the body or separating the cap from it.